This invention relates to the field of digital-to-analog converters and, more particularly, relates to expanding the precision of a digital-to-analog converter that is limited to a finite number of bits.
In the computer and telecommunications context, it is well known that electrical data signals are frequently characterized as being in either analog or digital form. In addition, the use of devices to convert electrical signals from one form to the other have been known for many years. These converters, known generally as either xe2x80x9cdigital-to-analogxe2x80x9d converters or xe2x80x9canalog-to-digitalxe2x80x9d converters, are used for a variety of purposes and in a variety of applications, including modems, telephones, music and video recording and reproduction equipment, and virtually any electronic device that must interface with multiple types of technology such as digital or analog technology.
Micro-controllers, a microprocessor and other general circuitry on the same substrate, often provide digital-to-analog or analog-to-digital circuitry. In addition, integrated circuit manufactures often incorporate digital-to-analog and/or analog-to-digital capabilities into general purpose and custom integrated circuits. In such micro-controllers and custom integrated circuits, the designers are typically limited in the amount of space or circuitry that can be included on a single substrate or the number of input and output pins of the integrated circuit. Due to these and other constraints, the precision of digital-to-analog and analog-to-digital converters are often limited. A typical digital-to-analog or analog-to-digital converter will be limited to a certain number of bits, such as eight bits.
When a product designer uses a micro-controller or a general purpose integrated circuit, the designer is limited to the precision of the analog-to-digital or digital-to-analog converter that is included with the integrated circuit. However, in certain circumstances, a higher degree of precision may be required than what is provided with the analog-to-digital or digital-to-analog converter provided with the micro-controller or general purpose integrated circuit. When such a design situation arises, the designer is forced to either utilize an external analog-to-digital or digital-to-analog converter, or try to find an integrated circuit with a more precise analog-to-digital or digital-to-analog converter.
One typical situation in which this arises is when a digital-to-analog converter is used to control the frequency of a transmitter. For example, a newer 1900 megahertz telephone, when compared to an older 800 megahertz phone, requires an increased frequency resolution that is small enough to meet a 200 hertz maximum error for a TMDA signal. This control range could be accomplished in older 800 megahertz telephones by utilizing an 8-bit digital-to-analog converter. While continuing to use an 8-bit digital-to-analog converter with the high-band telephone, it is not possible to obtain a small enough frequency increment range to control the accuracy of the signal. Thus, it is clear that there is a need in the art for method to expand the precision of an digital-to-analog converter without requiring a complete redesign of a product by forcing the selection of a new integrated circuit with an digital-to-analog converter having a higher precision.
The present invention solves the above-described problem by providing a circuit for increasing the precision or resolution of a digital-to-analog converter by utilizing a simple and elegant circuit external to the digital-to-analog converter.
More specifically, the present invention includes a circuit for increasing the precision of a digital-to-analog converter. The circuit includes an N-bit digital-to-analog converter having a digital signal input and an analog signal output and a translating circuit having an analog signal input electrically coupled to the analog signal output of the N-bit digital-to-analog converter, an analog signal output and a bias enable input. In operation, the N-bit digital-to-analog converter receives an N-bit digital signal on the digital signal input and converts the N-bit digital signal into a first analog output signal having 2N possible values over a first voltage range. This signal is then provided to the output of the N-bit digital-to-analog converter.
When the bias enable input is in a first state, the translating circuit translates the first analog output signal into a second analog voltage having 2N possible values over a second voltage range. This second voltage range has a smaller maximum value than maximum value of the first voltage range. When the bias enable input is in a second state, the translating circuit translates the first analog output signal into a second analog voltage having 2N possible values over a third voltage range. This third voltage range has a larger minimum value than the minimum value of the first voltage range. Thus, precision of the digital-to-analog converter is available for two ranges that are smaller than the original range, thereby increasing the precision of the digital-to-analog converter.